One purpose of this study is to investigate the effects of intensive insulin therapy on fuel and energy homeostasis and metabolic efficiency during exercise in IDDM, in order to evaluate their contribution to the excessive weight gain and exercise-induced hypoglycemia in intensively treated individuals with IDDM. A second purpose is to evaluate the effects of intensive insulin treatment in IDDM on FFA metabolism during exercise and the mechanisms through which treatment-associated alterations in fat metabolism affect glucose homeostasis during exercise in IDDM.